“…Some studies on the acute or sub-chronic action of antidepressant drugs showed that opioid antagonists can block the antidepressant-induced analgesia (Reichenberg et al, 1985;Valverde et al, 1994;Gray et al, 1998;Su and Gebhart, 1998;Schreiber et al, 1999Schreiber et al, , 2002Marchand et al, 2003c;Ortega-Alvaro et al, 2004;Mico et al, 2006;Benbouzid et al, 2008a,b), suggesting the involvement of the opioid system. On the contrary, other studies showed no effect of opioid antagonists on antidepressant drug action (Pick et al, 1992;Fuchs et al, 1996;Ghelardini et al, 2000;Marchand et al, 2003a,b).…”